definitly recommend upgrading the equipment between your steering wheel and your seat.
With the hardware you already have id make sure you have an effective tune, the 08+ arent super happy with CIA without a proper tune.
as far as rallycross is concerned id look into a nice light bar, something you can mount a protective skid plate to in the future and something that pleases your eye. if your also planning on using it as your DD id grab some flaps to protect the side of your paint : )
13 WRX Hatch - Torqued Performance Stage 1+
Slow is Smooth > Smooth is Fast